The apparatus relates to the separation of organic and inorganic substances from industrial wastewater assisted by electrochemical reactions.
The apparatus also relates to the recovery of noble and non-noble metals from solutions to be recovered as metallic deposits inside of the apparatus or as metallic particles suspended in one or more solutions leaving the apparatus.
Industrial wastewater treatment often involves separation of metals in solution, metal complexing agents, other anions and cations, oils, and reduction of COD.
Metals are ultimately separated by precipitation as hydroxides. Metal complexing agents have to be partially decomposed before one or more metals in solution can be removed. The decomposition of said complexing agents often involves oxidizing and reducing chemicals. Oxidizing chemicals are also used to partially decompose other anions and cations, organic matter and to lower the BOD and COD of the solution. Oil emulsions need to be broken by chemical and physicochemical reactions before they can be separated. Reducing chemicals are used to partially decompose anions and cations and to reduce Chromium from oxidation state 6+ to oxidation state 3+ rendering insoluble Chromium compounds.
Oxidizing chemicals are expensive and present handling and storage inconveniences. Reducing chemicals are also expensive and present similar inconveniences. A separate agitated vessel adequately sized and equipped is needed for each reaction that needs to take place. Flow-rate, addition of chemicals, and pH needs to be monitored and controlled in each vessel. Equipment is necessary to capture and manage any gases evolved from chemical decomposition reactions. Depending upon metal ion concentration and volume of wastewater to treat a substantial volume of metal hydroxide sludge could be generated presenting an additional handling, storage and disposal burden. The Handbook of Effluent Treatment and Recycling for the Metal Finishing Industry L Hartinger, pages 314-394 explains all the equipment frequently needed for continues and batch industrial wastewater treatment installations. U.S. Pat. Nos. 5,093,007, 4,420,401 and 4,009,101 are examples of industrial wastewater treatment schemes that also give an idea of all the equipment needed to treat a multiple contaminant aqueous effluent.
Recovery of a metal from an aqueous solution that contains ions of said metal by electrolysis involves immersing one or more positively charged electrodes (anodes) and one or more negatively charged electrodes (cathodes) in said solution and impressing across the electrodes of different polarity a direct current voltage of sufficient magnitude to effect migration of metal-ions and deposition of metal over the electrode surfaces.
It is well known that the efficiency of metal recovery by electrolysis from a solution is affected by factors like solution composition, temperature, metal-ion concentration, pH, and the level of agitation in the solution between anodes and cathodes. Anode and cathode surface characteristics, distance between anode and cathode, anode and cathode shape, anode and cathode surface composition, electrode arrangement and electric current profile also have influence over the efficiency of metal recovery from a solution.
It is well known that in Zinc, copper, nickel and other non-ferrous metals refineries around the world, the apparatus most widely used at industrial scale for metal recovery from a solution of its ions by electrolysis is what is mostly known as a ‘liberator cell’. A liberator cell consists of an open top rectangular tank fitted with square flat anode and cathode plates disposed vertically face to face. The liberator cell is preferred because of its simplicity of design and low operation cost. Its open top tank configuration allows more than one electrode plate to be lifted from the cell in a single operation, the flat electrode plates are simple to manufacture and metal deposits over flat electrode plates are easy to strip. Electrodes handling and stripping operations are usually automated rendering high productivity with minimum labor. The liberator cell though has important drawbacks. Its design makes gas and acid mist emission control difficult, agitation in the cell is limited, and the cell has a low liquid specific velocity. The two later conditions limit the specific current density that can be applied through the cell. Therefore low current efficiencies and metal hydroxide deposits can be expected in the electrolysis of low metal ion concentration solutions and because metal hydroxides adhere poorly to the cathodes they fall to the bottom of the cell and periodic shut downs for cell cleaning are needed.
Examples of other metal recovery apparatuses patented over the years are U.S. Pat. Nos. 6,451,183, 5,873,986, 5,753,099, 5,529,672, 5,421,977, 5,340,457, 5,102,522, 3,936,363, 3,751,351, 3,728,244. Although each one displays unique features and capabilities, they are not meant for quick and easy opening and closing for metal removal and cleaning and except for U.S. Pat. No. 6,451,183 these designs are not meant for high production output with low labor utilization.